Alkyl transfer of alkyl aromatics with metals of groups v-b,vii-b,i-b,and ii-b on boria-alumina

ABSTRACT

A PROCESS FOR THE ALKYL TRANSFER OF ALKYL AROMATICS, INCLUDING CONTACTING AN ALKYL AROMATIC FEED MATERIAL, SUCH AS TOLUENE, WITH A CATALYST COMPRISING A METAL SELECTED FROM GROUP I-B, SUCH AS COPPER OR SILVER,GROUP II-B, SUCH AS ZINC OR CADMIUM, GROUP V-B, SUCH AS VANADIUM, AND GROUP VII-B, SUCH AS MANAGANESE, AND BORIA DEPOSITED ON AN ALUMINA BASE AT A TEMPERATURE OF ABOUT 800 TO 1100*F., A PRESSURE OF ABOUT 0 TO 2000 P.S.I.G., AND A LIQUID HOURLY SPACE VELOCITY OF ABOUT 0.1 TO 10, AND IN THE PRESENCE OF HYDROGEN INTRODUCED AT A RATE OF ABOUT 1 TO 10 MOLES HYDROGEN PER MOLE OF HYDROCARBON FEED. PROMOTERS SELECTED FROM GROUP I, GROUP II, GROUP IV, AND THE RARE EARTH METALS OF THE PERIODIC SYSTEM MAY BE ADDED TO THT CATALYST. DEACTIVATED CATALYST MAY BE PERIODICALLY REJUVENATED BY CALCINATION IN AN ATMOSAROMATIC FEED MATERIAL AND PURGING WITH HYDROGEN AND THE CATALYST CAN BE REACTIVATED BY CALCINATION IN AN ATMOSPHERE SUCH AS AIR. WHERE TOLUENE IS THE FEED, THE ALKYL TRANSFER PRODUCT MAY BE DISTILLED TO SEPARATE BENZENE, TOLUENE AND XYLENES, THE TOLUENE MAY BE RECYCLED TO THE ALKYL TRANSFER STEP, THE XYLENES MAY BE CRYSTALLIZED TO SEPARATE PARA-XYLENE FROM THE REMAINING XYLENES, THE MOTHER LIQUOR FROM THE CRYSTALLIZATION STEP MAY THEREAFTER BE ISOMERIZED TO READJUST THE PARA-XYLENE CONTENT AND THE PRODUCT OF THE ISOMERIZATION MAY BE RECYCLED TO THE CRYSTALLIZATION ZONE.

United States Pat ABfiTlRACT OF THE DHSCLOSURE A process for the alkyltransfer of alkyl aromatics, including contacting an alkyl aromatic feedmaterial, such as toluene, with a catalyst comprising a metal selectedfrom Group I-B, such as copper or silver, Group IIB, such as zinc orcadmium, Group VB, such as vanadium, and Group VII-B, such as manganese,and boria deposited on an alumina base at a temperature of about 800 to1100 F., a pressure of about to 2000 p.s.i.g., and a liquid hourly spacevelocity of about 0.1 to 10, and in the presence of hydrogen introducedat a rate of about 1 to moles hydrogen per mole of hydrocarbon feed.Promoters selected from Group I, Group II, Group IV, and the rare earthmetals of the Periodic System may be added to the catalyst. Deactivatedcatalyst may be periodically rejuvenated by discontinuing theintroduction of aromatic feed material and purging with hydrogen and thecatalyst can be reactivated by calcination in an atmosphere such as air.Where toluene is the feed, the alkyl transfer product may be distilledto separate benzene, toluene and xylenes, the toluene may be recycled tothe alkyl transfer step, the xylenes may be crystallized to separatepara-xylene from the remaining xylenes, the mother liquor from thecrystallization step may thereafter be isomerized to readjust thepara-xylene content and the product of the isomerization may be recycledto the crystallization zone.

BACKGROUND OF THE INVENTION The present invention relates to a processfor the catalytic conversion of hydrocarbons and, more particularly, toa process for the catalytic alkyl transfer of alkyl aromatics.

Aromatic hydrocarbons, such as benzene, naphthalene, and their alkylderivatives are important building blocks in the chemical andpetrochemical industries. For example, benzene and its derivatives havenumerous uses; cyclohexane is utilized in nylon production; naphthaleneis utilized in the production of phthalic anhydride for alkyd resins,etc.; para-xylene can be used for the production of terephthalic acidwhich, in turn is utilized in the production of synthetic resins, suchas dacron, mylar, etc., etc.

For many years, the primary source of such aromatic hydrocarbons hasbeen coal tar oils obtained by the pyroolysis of coal to produce coke.Such tar oils contain principally benzene, toluene, naphthalene,methylnaphthalene and para-xylene. Benzene may be produced from suchoils by direct separation, such as distillation techniques, thepara-Xylene may be separated by crystallization, and the naphthalenefractions by direct separation techniques. Further alkyl derivatives ofbenzene and naphthalene can be converted to increased volumes of benzeneand naphthalene by hydrodealkylation.

More recently, however, the petroleum industry has become a leadingsource of these aromatic hydrocarbons. The reason for this has been theavailability of the catalytic reforming process in which naphthenehydrocarbons are dehydrogenated to produce a reformate rich in aromaticsand more efficient processes for separating the aromatics from thereformate.

Some years ago, there was a high demand for toluene which was used inthe production of TNT. This led to the building of substantialfacilities for its production. However, the advent of nuclear and fusionweaponry and the use of diesel oil-ammonium nitrate explosives has lefttoluene in substantial over-supply, since the only major uses of tolueneare as a solvent, the production of toluene diisocyanates and theproduction of benzene. This has resulted in extensive eiforts to developmethods for converting toluene to benzene. One method of convertingtoluene to benzene is by the previously mentioned hydrodealkylation.

Dealkylation has the primary disadvantage that methane is a majorproduct. Volume yields of benzene are therefore low and carbondeposition on the catalyst is high. The large amounts of methane, whileuseful as a fuel, require expensive techniques for the removal of themethane from the circulating hydrogen stream utilized in thehydrodealkylation. In addition, large quantities of hydrogen areconsumed in the dealkylation process and hydrogen is often in shortsupply and expensive to produce. Finally, where catalysts are used inthe process, carbon laydown on the catalyst is a serious problem.

A more profitable reaction for changing alkyl aromatics to otheraromatic products is an alkyl transfer reaction. An alkyl transferreaction is a process wherein alkyl groups are caused to be transferredfrom the nuclear carbon atoms of one aromatic molecule to the nuclearcarbon atoms of another aromatic molecule. By way of example, anaromatic hydrocarbon molecule containing one nuclear alkyl substituent,such as toluene, may be treated by disproportionation to produce anaromatic hydrocarbon with no alkyl substituents, namely, benzene, andaromatic hydrocarbon molecules with two nuclear alkyl substituents,namely xylenes. Similarly, product ratios may be shifted bytransalkylation of Xylene and benzene to toluene. Such an alkyl transferreaction has distinct advantages: methane is not produced, but instead,valuable aromatic hydrocarbons are produced in addition to the desiredaromatic hydrocarbon. As a result, there is very little loss of productin alkyl transfer as opposed to hydrodealkylation.

Alkyl transfer may be carried out thermally. However, thermal alkyltransfer results in demethylation due to cracking and hydrogenation,ultimately resulting in low yields of desired aromatics. On the otherhand, catalytic alkyl transfer has not been highly successful since itrequires an active, rugged, acidic catalyst. Typical catalysts are solidoxides, such as silica-alumina, silica-magnesium, etc. These materials,however, are not active enough to promote disproportionation at highconversion rates. In addition, as is the case in hydrodealkylation,carbon deposition on the catalyst and its affect on catalyst activitywith time is a severe problem.

It is therefore an object of the present invention to provide animproved process for the conversion of alkyl aromatics. Another objectof the present invention is to provide an improved process for the alkyltransfer of alkyl aromatics. Yet another object of the present inventionis to provide an improved process for the disproportionation of tolueneto produce benzene and xylenes. Another and further object of thepresent invention is to provide an improved process for thedisproportionation of alkyl aromatics which utilizes a. novel catalystsystem. Another object of the present invention is to provide animproved process for the disproportionation of alkyl aromatics with acatalyst system resistant to carbon laydoWn. A further object of thepresent invention is to provide an improved process for the catalyticdisproportionation of alkyl aromatics utilizing a Group I-B, II-B, VB orVIIB metal and boria on an alumina base. A further object of the presentinvention is to provide an improved process for the disproportionationof alkyl aromatics utilizing critical conditions of temperature andpressure which produce maximum disproportionation and conversion of onearomatic to another. Still another object of the present invention is toprovide an improved process for the conversion of toluene to benzene andxylenes and conversion of metaand ortho-xylenes to additionalpara-xylene. These and other objects and advantages of the presentinvention will be apparent from the following detailed description.

SUMMARY OF THE INVENTION Briefly, in accordance with the presentinvention, alkyl transfer of alkyl aromatics comprises contacting analkyl aromatic feed material with a catalyst comprising a metal of GroupI-B, II-B, V-B or VIIB of the Periodic System or mixtures thereof andboria deposited on an alumina base. Further improvement of the catalystis obtained by adding a Group I, Group II, Group IV, a Rare Earth metalor mixtures thereof. Further improvements of the process are obtained bymaintaining the temperature between about 800 and 1100 F. and thepressure between about and 2000 p.s.i.g. Where toluene is the feed,additional para-Xylene is produced by isomerizing orthoand meta-xylenes.

BRIEF DESCRIPTION OF THE DRAWINGS The drawing shows a flow diagram of aprocess system in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION Alkyl aromatic feed materials foruse in accordance with the present invention can be any alkyl aromatichaving at least one transferrable alkyl group. Primary materials arealkyl aromatics having from 7 to 15 carbon atoms, mixtures of such alkylaromatic hydrocarbons, or hydrocarbon fractions rich in such alkylaromatic hydrocarbons. Such feeds include monoand di-aromatics, such asalkyl benzenes and alkyl naphthalenes. Preferably, the alkyl groupshould contain no more than about 4 carbon atoms. A preferred feed inaccordance with the present invention is toluene. Accordingly,disproportionation of toluene will be referred to hereinafter in thedetailed description.

The process of the present invention should be conducted at atemperature between about 800 and 1100 F and preferably between 850 and1000 F. It has been found in accordance with the present invention thatbelow this temperature range, substantially decreased conversion occursdue to hydrogenation. On the other hand, when operating above thistemperature range, thermal demethylation occurs. The pressure utilizedin accordance with the present invention has also been determined to bea critical factor. Accordingly, the process should be carried outbetween about 0 and 2000 p.s.i.g. and preferably, between 300 to 600p.s.i.g. It has been found that below the desired pressure range,conversion is low and the aromaticity of the product is high. On theother hand, at higher pressures, conversion is high, but liquidrecoveries are low due to hydrogenation and hydrocracking. A liquidhourly space velocity between about 0.1 and 10, and preferably between0.25 and 1.(), should be utilized and a hydrogen-to-hydrocarbon moleratio between about 1 and to l and preferably between 2 and 4 to 1 isdesired.

The high severity conditions required to obtain disproportionation ofalkyl aromatics, particularly the disproportionation of toluene, hasbeen found to lead the catalyst deactivation due to selective adsorptionand condensation of aromatics on the catalyst surface and carbon laydownon the catalyst. It was found that the condensation and adsorption ofaromatics on the catalyst is a tem.- porary poison and that thiscondition can be alleviated by utilizing high hydrogen partialpressures. In addition, this temporary deactivation of the catalyst canbe overcome to completely rejuvenate the catalyst to near virginactivity by hydrogen-purging of the catalyst in the absence of aromatichydrocarbon feed. While coke or carbon deposition on the catalyst is apermanent poison, it has been found, in accordance with the presentinvention, that carbon laydown can be decreased by utilizing thecatalysts of the present invention. Further, it was found that whenthese catalysts become deactivated by carbon laydown, they can berestored to near virgin activity by regeneration in air.

The catalyst employed in accordance with the present invention is amulti-faceted cure for many of the ills of catalytic disproportionationreactions. First, it has been found that boria deposited on an aluminabase is vastly superior to a silica-alumina base catalyst; the formerconsistently proving to be twice as active as the latter. The amount ofboria deposited on the alumina may vary between about 5 and 25% byWeight of the finished catalyst. The alumina is preferably a gammaalumina. Such gamma aluminas are very stable up to temperatures of about1800 F. One such alumina, Boehmite, may be prepared in a variety ofways, one of the simplest being the addition of ammonium hydroxide to aWater solution of aluminum chloride. The material originallyprecipitated is an amorphous alumina flock which rapidly grows tocrystal size yielding crystalline Boehmite. Aging of Boehmite inammonium hydroxide solution transforms the Boehmite first to themeta-stable Bayerite and finally to the highly stable Gibbsite. TheBayerite is preferred and may be in its betaor etaform.

The active metal added to the boria-alumina may include a Group *I-Bmetal, such as copper, silver, etc., a Group IIB metal, such as zinc,cadmium, etc., a Group V-B metal, such a vanadium, etc., a Group VII-Bmetal, such as manganese, etc., or mixtures of these metals. Thesemetals are preferably in their oxide form. The active metalconcentration may be between about 2 and 20% and preferably is between 4and 6% by wei ht of the finished catalyst.

It has also been found that conversion may be improved and, moresignificantly, carbon laydown on the catalyst may be reduced by theaddition thereto of a promoter. Such promoters may be selected fromGroup IA of the Periodic System, such as potassium, rubidium, cesium,etc., Group II-A of the Periodic System, such as calcium, magnesium,strontium, etc., a Rare Earth metal of the Periodic System, such ascerium, thorium, etc., a Group IV metal of the Periodic System, such astin or lead, or mixtures of these, and particularly mixtures of a GroupIV metal with one of the other groups mentioned. The promoters arepreferably in their oxide form and are present in amounts of about 1 to15% by weight based on the weight of the finished catalyst.

The catalysts may be prepared by techniques Well known in the art. Forexample, such preparation may include coprecipitation or impregnationtechniques. One can employ extrudates or pellets for impregnation orpowders followed by pelletization or extrusion to yield the finishedcatalyst. When employing impregnation techniques, the metals may beadded to the base singly or in combination, utilizing water solublesalts such as borates, boric acid, halides, nitrates, sulfates,acetates, etc. Easily hydrolyzed salts can be kept in solution Withoutdecom position by employing the appropriate inorganic acids. Well-knownprocedures for drying and calcination of the catalyst will also beemployed. For example, vacuum drying at a temperature of about 250 F.and calcination in an oxidative, neutral or reductive atmosphere,utilizing a calcination temperature of about 800 to 1200 F. can bepracticed.

Preparation of a specific catalyst is illustrated below.

To 200 ml. of distilled water was added 25 g. of vanadyl sulfate and 31g. of boric acid. The solution was heated until all the metal salts wentinto solution. This hot solution was added slowly to 250 ml. of bayeritealumina and allowed to stand for 15 minutes. At the end of this period,the liquid was decanted from the impregnated alumina. The resultingcatalyst was dried at 250 F. for 1 hour in a vacuum oven and thencalcined in a muffle furnace at 950 F. in air for 16 hours. This yieldsthe following composition:

5% V O -10% B O -Al O The use of vanadia as an active metal isillustrated in the following tables.

In Table I, vanadia is compared with boria-alumina containing no activemetal and boria-alumina having platinum as an active metal, as acatalyst for disproportionation of toluene.

TABLE I 950 F., 800 p.s.i.g. 0.5 LHSV, 3/1. Hg/I-IC 10%13203 5.0% V2050.3 pt. 10% A 203 10% 13203-111203 13203-181203 Catalyst Conversionweight,

percent ieed 41. 4 45. 5 36. 5 A conversion weight,

percent per hour 3. 0. 0 5. 0

TABLE II 10% V205 V205 Catalyst 10% B203-Alz03 13203-21120,;

Conditions (950 F., 800 p.s.i. 0.5

LHSV, 3/1 Hg 16 2. 0

Conversion weight, percent feed A conversion Weight, percent per hour 0In accordance with the present invention, an integrated process for theproduction of benzene and para-xylene from toluene can be carried outwith resultant high yields of these two valuable products. This processis best described by reference to the drawing.

In accordance with the drawing, toluene is introduced to the systemthrough line 10, hydrogen is added through line 12 and these materialsare passed over the catalyst of the present invention in thedisproportionation reactor 14. The effluent passing through line 16 ispassed to a flash drum for the removal of hydrogen and any light gasesproduced. These materials are discharged through line 18. Since littleor no demethanation occurs, the hydrogen is substantially pure and maybe recycled to the disproportionation reaction without furthertreatment. However, in some instances, further purification of thehydrogen is necessary before recycle or reuse. The liquid product passesthrough line 20 to a first distillation unit 22. In distillation unit22, benzene is recovered as an overhead through line 24. The bottomsproduct from distillation unit 22 passes through line 26 to a seconddistillation unit 28. In distillation unit 28, toluene is removed as anoverhead product and recycled to the disproportionation section through.line 30. The bottoms product from distillation unit 28 is a mixture ofxylenes which is discharged through line 32. This product may bewithdrawn, as such, through line 34. Preferably, however, the xyleneproduct is passed through line 36 to crystallization unit 38. Incrystallization unit 38, paraxylene is selectively removed and withdrawnthrough line 40. The mother liquor from the crystallization section ispassed through line 42 to an isomerization unit 44. Hydrogen is addedthrough line 46. In the isomerization unit 44, the equilibriumconcentration of para-xylene is re-established and the material may thenbe recycled through line 48 to crystallization unit 38 for furtherpara-Xylene separation.

The isomerization reaction should be carried out under more mildconditions than the disproportionation. Catalysts useful in thedisproportionation reaction might also be used in the isomerization orconventional catalysts, such as platinum on silica-alumina, can be used.The isomerization may be carried out at temperatures of about 500 to 900F., and preferably 550 to 650 F., pressure The followin tables furtherexem 1i the resent in- 5 of 50 to 2000 p.s.i.g., and preferably 300 to600 .s.i.

g vention. at a liquid hourly space velocity of 0.1 to 10, and utilizingTABLE III a hydrogen-to-hydrocarbon mole ratio between about 1 10 B O 10B O and 20 to 1. Catalyst 2% 1 5,5 3, 2% fi ag When reference is madeherein to the Periodic System r d T 1 T 1 T I 59 of Elements, thepartlcular groupings referred to are as 4 u n 0 235 555 Queue 0 setforth in the Periodic Chart of the Elements in The g p ra F 338 25g ,288Merck Index, Seventh Edition, Merck & Co., Inc., 1960. Q5 Q5 1 The termalkyl transfer of alkyl aromatics as used An f z l g 3 3 3 herein ismeant to include disproportionation and trans- FF 0 1 0 .25 b g p8alkylation. Disproportionatron, in turn, is meant to ing f 13-3 cludeconversion of two moles of a single aromatic, such m 5316 ifz astoluene, to one mole each of two different aromatics, 3i such as xylenesand benzene. Transalkylation is meant to Conversion i'tbiiriiIIIIII4014. 2828 24.5 include conversion of one mole each of two different 60aromatics, such as xylenes and benzene, to one mole of TABLE IV 50110-10 5 VzO5-2 111102 5 VgO5-2 S110 5 7205-2 K20 5 7205-2 060 B203 10B2 s- 20s- 10 20s- 20s- Catalyst A1203 A1203 A1203 A1203 A1203 FeedToluene Toluene Toluene Toluene Toluene Conditions:

Temp, F 1,000 1,000 1, 000 1, 000 1, 000 Pressure, p.s.i.g 800 800 800800 800 LHSV 0.5 0.5 0.5 0.5 0.5 Hz/HC 3/1 3/1 3/1 3/1 3/1Recoveryvolume percent..- 86 93 88 88 92 Toluene conversion 55 34 19 1533 Product distribution:

5.8 3.5 0.2 0.3 1.0 28.7 19.7 5.2 2.7 10.4. 52. 5 71. 2 92. 3 96.8 73. 212.0 5.3 2.2 0.2 8.6 xy1ene 1. 0 0.3 0. 1 0.8 Carbon on catalyst, weightpercent feed 2. 5 0. 0. 45 0. 23 0. 71

a single different aromatic such as toluene. The alkyl transfer definedabove is also to be distinguished from isomerization Where there is notransfer of alkyl groups from one molecule to another but simply ashifting of alkyl group around the aromatic ring, such as isomerizationof xylenes, or rupture of the ring of the alkyl side chain andrearrangement of split-off carbon atoms on the same molecule. The alkyltransfer is also to be distinguished from a hydrogen transfer reaction,such as the hydrogenation of aromatics, the dehydrogenation ofcyclo-parafiins and like reactions.

We claim:

1. A process for the alkyl transfer of alkyl aromatics; comprising,contacting an alkyl aromatic feed material and hydrogen with a catalystcomprising about 2 to 20% by Weight of a metal selected from the groupconsisting of Group IB, Group IIB, Group V-B and Group VII-B of thePeriodic System and mixtures thereof, and about 1 to 15% by weight ofboria deposited on an alumina base, under conditions sufiicient to causesaid transfer disproportionation of said alkyl aromatics.

2. A process in accordance with claim 1 wherein the metal is a metal ofGroup IB.

3. A process in accordance with claim 1 wherein the metal is a metal ofGroup II-B.

4. A process in accordance with claim 1 wherein the metal is a metal ofGroup VB.

5. A process in accordance with claim 1 wherein the metal is a metal ofGroup VII-B.

6. A process in accordance with claim 1 wherein the feed materialcontains substantial volumes of toluene.

7. A process in accordance with claim 6 wherein unconverted toluene isseparated from the alkyl transfer product and said unconverted tolueneis recycled to the disproportionation step.

8. A process in accordance with claim 6 wherein xylenes are separatedfrom the alkyl transfer product and paraxylene is separated from saidxylenes.

9. A process in accordance with claim 8 wherein the xylenes remainingafter the separation of para-xylene are subjected to isomerizationconditions sufficient to produce additional para-xylene.

10. A process in accordance with claim 1 wherein the flow of feedmaterial through the catalyst is interrupted periodically and teh flowof hydrogen is continued for a time sufficient to reactivate thecatalyst.

11. A process in accordance with claim 1 wherein the flow of feedmaterial and hydrogen through the catalyst is discontinued and thecatalyst is calcined in air under conditions sufficient to reactivatethe catalyst.

12. A process in accordance with claim 1 wherein the catalystadditionally contains about 1 to 15% by weight of a metal selected fromthe group consisting of Group IA, Group IIA, Group IV and the rare earthmetals of the Periodic System and mixtures thereof.

References Cited UNITED STATES PATENTS 2,795,629 6/1957 Boedeker 2606683,260,764 7/1966 Kovach et al 260-672 DELBERT E. GANTZ, Primary ExaminerG. E. SCHMITKONS, Assistant Examiner US. Cl. X.R.

